The detection and analysis of samples has become increasingly important in a variety of fields and industries, including those relating to healthcare, environmental applications, laboratory research and national defense. For example, the detection of sample materials such as chemical or biological species is useful for identifying the samples and/or characterizing a particular solution in which the samples are present. In the healthcare industry, these approaches are useful in analyzing blood and other fluids. In environmental applications, these approaches are useful in analyzing lakes, rivers, water supplies and treatment facilities.
Approaches to sample detection have been limited for a variety of reasons. In many applications, sample detection has required expensive labeling and detection equipment. In addition, while it is often desirable to detect samples in a variety of environments, many sensors are not amenable to use with certain environments. For instance, detecting analytes has been challenging in environments susceptible to moisture. Detection has been particularly challenging under conditions involving analytes that are in solution such as an aqueous solution, as often is the case for comprehensive environmental monitoring and biological sensing.
One relatively economical and flexible device that has been used in sensing applications is the organic thin-film transistor (OTFT). OTFTs are useful for performing a variety of functions and offer unique characteristics desirable for many applications. See, e.g., Sze, S. M. Semiconductor Devices: Physics and Technology, 2nd edition; Wiley: New York, 1981. Generally, OTFTs are low in weight, flexible in application and inexpensive; as such, OTFTs are useful for a multitude of applications.
While OTFTs are useful for many applications, their manufacture and implementation for sensor applications has been challenging. Generally, OTFTs have not been suitable for applications involving exposure to moisture and aqueous solutions due to high operating voltages, degradation and delamination under aqueous conditions, and in particular under conditions that expose a significant portion of the OTFT to a solution. See, e.g., Someya, T., et al., Integration and response of organic electronics with aqueous microfluidics, Langmuir, 2002, 18(13): p. 5299-5302, incorporated herein by reference. Dielectric materials used in OTFTs have generally been susceptible to the formation of pinholes, which introduce undesirable characteristics. Many applications directed to the formation of OTFTs require relatively high temperature (e.g., over 150° C., or over 200° C.), which can present challenges to the implementation of certain materials. Other challenges to the formation of OTFTs relate to processing characteristics, including those related to the ease, consistency and quality of the manufacture of dielectric layers for OTFTs. For instance, many manufacturing approaches are characterized by undesirable moisture sensitivity, high reactivity, and rough surfaces. Still other challenges to the implementation of OTFTs are related to compatibility with different gate and channel materials, and with organic semiconductors.
These and other characteristics have been challenging to the design, manufacture and use of sensors and, in particular, of sensors used in moisture-susceptible environments.